Sertraline has two chiral centres and hence has four stereoisomeric forms, namely, the (1R,4R), (1S,4S), (1R,4S), and (1S,4R) isomeric forms of sertraline. Of these, the active stereoisomer for therapeutic purpose is the cis (1S,4S) isomer of formula 1.

Although a number of processes have been described for the production of setraline or intermediates used in the production of setraline, see U.S. Pat. No. 4,536,518, U.S. Pat. No. 4,556,676, U.S. Pat. No. 4,777,288 U.S. Pat. No. 4,839,104, WO98/15516, U.S. Pat. No. 5,196,607, U.S. Pat. No. 5,466,880, Tetrahedron, 48(47), 10239 (1992), WO95/15299, WO98/27050, Organic Lett., 1(2), 293 (1999), in all the methods described, eventual isomer separation is inevitable. These documents describe processes for producing sertraline and the disclosures in these documents illustrate the problems in producing optically pure sertraline and the resulting low yields and waste that arises due to production of unwanted isomers.
In U.S. Pat. No. 5,082,970 there is described a process for recycling the trans isomer of sertraline. However, this process appears only to isomerise only one of the two chiral centres of the trans isomer of sertraline.
In WO01/49638 and WO05/023752 there are described processes for the isomerisation of both chiral centres of setraline isomers. WO01/49638 requires that the amine first be oxidised to an imine. This imine intermediate is subjected to an isomerisation process at the benzylic chiral centre and then subsequently reducing the imine non-stereospecifically. WO05/023752 seeks to isomerise the benzylic chiral centre first before subjecting the amine to oxidation and reduction either directly of the imine or indirectly by reaction of the ketone with an amine and reduction of the imine so produced. Both of these methods suffer from the disadvantage that oxidation of amines to imines is difficult and not only requires the use of strong oxidants in stoichiometric amounts but often results in the production of unwanted ketone which adds to the complexity of the recycle.
It is therefore, the object of the present invention to develop an alternate simple process whereby the unwanted isomers, can be recycled to produce the desired cis (1S,4S) isomer in a simple manner which is commercially feasible.